1. Technical Field
The present invention relates in general to an improved hard disk drive and, in particular, to an improved system, apparatus, and method of assembling hard disk drive integrated lead suspensions to arm electronics cables in hard disk drives via additional degrees of freedom at the tail terminations.
2. Description of the Related Art
Generally, a data access and storage system consists of one or more storage devices that store data on magnetic or optical storage media. For example, a magnetic storage device is known as a direct access storage device (DASD) or a hard disk drive (HDD) and includes one or more disks and a disk controller to manage local operations concerning the disks. The hard disks themselves are usually made of aluminum alloy or a mixture of glass and ceramic, and are covered with a magnetic coating. Typically, one to six disks are stacked vertically on a common spindle that is turned by a disk drive motor at several thousand revolutions per minute (rpm).
A typical HDD also utilizes an actuator assembly. The actuator moves magnetic read/write heads to the desired location on the rotating disk so as to write information to or read data from that location. Within most HDDs, the magnetic read/write head is mounted on a slider. A slider generally serves to mechanically support the head and any electrical connections between the head and the rest of the disk drive system. The slider is aerodynamically shaped to glide over moving air in order to maintain a uniform distance from the surface of the rotating disk, thereby preventing the head from undesirably contacting the disk.
Typically, a slider is formed with an aerodynamic pattern of protrusions on its air bearing surface (ABS) that enables the slider to fly at a constant height close to the disk during operation of the disk drive. A slider is associated with each side of each disk and flies just over the disk's surface. Each slider is mounted on a suspension to form a head gimbal assembly (HGA). The HGA is then attached to a semi-rigid actuator arm that supports the entire head flying unit. Several semi-rigid arms may be combined to form a single movable unit having either a linear bearing or a rotary pivotal bearing system.
The head and arm assembly is linearly or pivotally moved utilizing a magnet/coil structure that is often called a voice coil motor (VCM). The stator of a VCM is mounted to a base plate or casting on which the spindle is also mounted. The base casting with its spindle, actuator VCM, and internal filtration system is then enclosed with a cover and seal assembly to ensure that no contaminants can enter and adversely affect the reliability of the slider flying over the disk. When current is fed to the motor, the VCM develops force or torque that is substantially proportional to the applied current. The arm acceleration is therefore substantially proportional to the magnitude of the current. As the read/write head approaches a desired track, a reverse polarity signal is applied to the actuator, causing the signal to act as a brake, and ideally causing the read/write head to stop and settle directly over the desired track.
In the prior art, the current preferred method of accomplishing the termination of the integrated lead suspension (ILS) to an arm electronics (A/E) cable of the disk drive is to use a solder joint. The solder joint is a right-angle fillet joint, formed between the ILS tail and the A/E cable. The current technology for forming this joint is well documented in U.S. Pat. No. 6,212,046, to Albrecht, et al. Current solder terminations rely upon flattened solder pads on the ILS tail to accommodate height variations of the mating A/E solder pads. The height variations can be due to manufacturing variations in the solder pads on the A/E cable and/or solder pad variations on the ILS tail. Angular displacement of the ILS tail with respect to the A/E solder pads can also create height variations. The flattened solder pads on the ILS tail will increase their height upon heating as surface tension of the molten solder pulls the flattened pads into approximate spheres. This increase in height allows the molten solder on the ILS tail to contact the mating solder pads on the A/E cable and form a joint. Although the current process is fairly robust, it has an associated rework rate due to excessive gaps between mating pads due to aforementioned causes. Another limitation to this process is that the ILS manufacturers are limited to a solder screening process to assure that a sufficient volume of solder is applied.
Referring to FIGS. 1–7, a prior art design for an ILS tail 11 is shown. ILS tail 11 has a single large solid platform 10 (FIG. 6) of steel to support the copper pads 14 (eight shown in FIG. 5), with a single large solid insulator 13 (FIG. 7) or dielectric therebetween. Solder pads 15 are applied to copper pads 14 by a screening process. Ideally, the ILS tail 11 matches and interacts with the solder pads 17 (FIG. 3) on the A/E cable 19 and form a 90-degree fillet joint, as shown in FIG. 4. The ILS tails 11 are oriented horizontally and the A/E cable 19 is oriented vertically and, thus, are oriented at 90-degrees relative to each other. Initially, the ILS tails 11 are biased (e.g., sprung) against each other and restrained in this manner as they are inserted into the angled slots 23 formed in the A/E cable 19. When released, the solder pads 15 of the ILS tails 11 are loaded or biased (see arrows 21) against the solder pads 17 of the A/E cable 19.
As described in U.S. Pat. No. 6,212,046, and as shown in FIG. 5, each ILS tail 11 has a layer of steel 10, a layer of polyimide 13, copper pads 14, and flattened solder pads 15. When heated, the solder pads 15 become molten and increase in height. The molten state of the thick solder pads 15, in conjunction with the spring load of the ILS tail 11, allows the solder pads 15 to accommodate (within certain limits) any gaps or non-mating conditions between the ILS tails and the A/E cable 19. In the prior art, compliance between ILS pads and A/E cables is provided only for all of the pads in unison, which is primarily supplied by the cantilever spring action of the tails. The full laminate thickness of the tails acts as a spring for the tails. However, as shown in FIG. 5, the spring load 21 is unable to overcome all gaps 25 and non-mating conditions between the ILS tails 11 and the A/E cable 19. Although the conventional method described above for terminating ILS tails to A/E cables has been used in production since 1996, the need for rework or “touch-up” has not been overcome and still exists today. For example, at the pad level, the incidence of rework is relatively low (approximately 1.5% or less). However, when the rework rate is calculated at the head stack assembly level, the rework rate is sizable and can exceed 15%.
Although it would be desirable and even preferable to use a plating process on the ILS pads instead of the conventional and thicker solder screening process, the plating process forms pads that are an entire order of magnitude thinner than solder pads. As a result, plated pads produce a smaller volume of solder than what is required and provided by the currently preferred method of screened solder terminations. Consequently, the benefits of the plating process, which include less oxidation, elimination of the toxic material lead (Pb), and a greater choice of solder alloys, cannot be realized. Thus, an improved system, apparatus, and method of terminating ILS tails to A/E cables is needed that would allow the solder pads to be plated onto the ILS tails would be desirable.